An organic electroluminescence device has a simple structure, so that it has been expected as a luminescence device for the next generation display that is thinner, lighter, larger area and less costly. Thus, recently, the organic electroluminescence device has been studied hard.
As a driving method for driving the organic electroluminescence device, an active-matrix type of filed effect transistor (FET) that uses a thin film transistor (TFT) is considered to be advantageous in terms of operational speed and power consumption. On the other hand, as a semiconductor material for forming the thin film transistor, inorganic semiconductor materials such as a silicon semiconductor or a chemical compound semiconductor have been studied, but recently, an organic thin film transistor (organic TFT) that uses an organic semiconductor material has been also studied hard. The organic semiconductor material has been expected as a semiconductor material of the next generation. However, the organic semiconductor material has problems of a lower charge-transfer level and of a higher resistance, compared with the inorganic semiconductor material.
Regarding the filed effect transistor, a vertical FET structured type of static induction transistor (SIT) wherein the structure thereof is vertically arranged is recognized to be advantageous because a channel width of the transistor can be shortened, the whole electrode of the surface thereof can be effectively used so that rapid response and/or power enhancement can be achieved, and interface effect can be made smaller.
Accordingly, recently, based on the above advantageous features of the static induction transistor (SIT), an organic luminescence transistor composed of such an SIT structure and an organic electroluminescence device structure has been studied to be developed (for example, Kazuhiro Kudo, “Current Conditions and Future Prospects of Organic Transistor”, J. Appl. Phys. Vol. 72, No. 9, pp. 1151-1156 (2003); JP-A-2003-324203 (in particular, claim 1); JP-A-2002-343578.
FIG. 18 is a schematic sectional view showing an example of an organic luminescence transistor composed of an SIT structure and an organic electroluminescence device structure, described in the above document “Current Conditions and Future Prospects of Organic Transistor”. As shown in FIG. 18, the organic luminescence transistor 101 has a vertical type of FET structure wherein a source electrode 103 consisting of a transparent electrode film, a hole-transfer layer 104 in which slit-like Schottky electrodes 105 are embedded, a luminescent layer 106, and a drain electrode 107 are layered on a glass substrate 102 in this order.
As described above, in the composite type of organic luminescence transistor 101, the slit-like Schottky electrodes 105 are embedded in the hole-transfer layer 104. A Schottky barrier junction is formed between the hole-transfer layer 104 and the gate electrode 105, so that a depletion layer is formed in the hole-transfer layer 104. The expansion of the depletion layer is varied by the gate voltage (voltage applied between the source electrode 103 and the gate electrode 105). Thus, a channel width is controlled by varying the gate voltage, and an amount of generated charge is varied by controlling a voltage to be applied between the source electrode 103 and the drain electrode 107.
FIG. 19 is a schematic sectional view showing an example of an organic luminescence transistor composed of an FET structure and an organic electroluminescence device structure, described in JP-A-2002-343578. As shown in FIG. 19, the organic luminescence transistor 111 has a substrate 112, on which an assistance electrode 113 and an insulation layer 118 are layered. Then, an anode 115 is partially formed on the insulation layer 118. Furthermore, a luminescent material layer 116 is formed on the insulation layer 118 such that the luminescent material layer 116 covers the anode 115. A cathode 117 is formed on the luminescent material layer 116. An anode buffer layer 119 is formed on the anode 115. The anode buffer layer 119 has a function of allowing passage of holes from the anode 115 to the luminescent material layer 116 but blocking passage of electrons from the luminescent material layer 116 to the anode 115. In the organic luminescence transistor 111 as well, a channel width is controlled by varying a voltage to be applied between the assistance electrode 113 and the anode 115, and an amount of generated charge is varied by controlling a voltage to be applied between the anode 115 and the cathode 117.